1. Field of the Invention
The present invention relates to an epicyclic transmission particularly suited for driving zero turning radius vehicles.
2. Prior Art
Steering control for numerous vehicles depends on the difference of speed which can be obtained between two drive wheels. When turning, the inner wheel rotates more slowly than the outer wheel. Vehicles that can turn about a point midway between the two drive wheels are classified as zero turning radius (ZTR) vehicles. Such turning is accomplished by one drive wheel rotating in a forward direction as fast as the other drive wheel rotates in the reverse direction.
A commnonly used arrangement for achieving a zero turning radius is employing a hydraulic motor and an associated vehicle displacement pump for hydraulically driving each wheel of a ZTR vehicle, such as a riding-type lawn tractor. However, hydraulic systems have disadvantages such as flow problems and leakage loss which affect efficiency. Also, pressure pulses can occur in hydraulic systems causing noise.
The present invention overcomes the above-noted deficiencies resulting in a quiet transmission not requiring the precision components necessary for a hydraulic system.
The invention is an epicyclic transmission capable of use in a zero turning radius vehicle. A drive shaft is coupled to a wheel-driving output through an epicyclic gear arrangement which, as a unit, is capable of rotation about a longitudinal axis of the drive shaft while also rotating about its own axis which extends transverse to the drive shaft""s axis. A drive gear is joined to the drive shaft for rotation therewith. A driven gear is mounted on the drive shaft but is rotatable independently of the shaft""s rotation. The driven gear is operatively joined to the epicyclic gear arrangement. Facing surfaces of the drive and driven gears are provided with annular concavities. A friction disk extends between the concave surfaces of the facing gears. The disk is pivotally adjustable so as to adjust the locations along the concave surfaces which are engaged by the disk. Rotation of the drive gear is translated by the disk to control the speed and the direction of rotation of the driven gear dependent on the disk""s position. When the driven gear is rotated at a different speed than the drive gear, the driven gear imparts forces on the epicyclic gear causing it to rotate about the drive shaft""s axis at the same time the epicyclic gear rotates about its own axis. Such compound movement of the epicyclic gear permits the speed and direction of the wheel-driving output to be controlled as a function of the position of the friction disk.